This invention relates generally to the measuring art, and more specifically to a new and useful system using radiation, such as beta backscatter, for the automatic measurement of coating thicknesses on continuously moving strip, band and similar material.
The beta backscatter radiation technique for measuring ultra thin coating thicknesses is well known, being disclosed in U.S. Pat. No. 3,132,248, among others, and various types of apparatus have been developed for use in conjunction therewith. Often the workpiece is placed on a measuring table which has an apertured support for the workpiece in operative alignment with a radiation source and detector. See, for example, U.S. Pat. No. 3,115,577. Where it is either impractical or impossible to position the workpiece on such a table, a portable measuring probe is used, the portable probe being positioned either directly on the workpiece or on a separate supporting surface for such workpiece. U.S. Pat. No. 3,529,158 shows one type of portable probe.
Often it is desirable to measure the coating thickness on a continuously moving strip or band of material, for example as the coated material comes from the coating apparatus. This permits appropriate adjustments to be made in the coating process or apparatus, while the coated material is being produced. However, the measurement of moving material presents obvious problems, and is made more difficult when the material being measured is of an interrupted nature, for example a strip of semi-conductor contacts, because of the required positioning of the measuring probe relative to the segmented material under test if accurate measurements are to be obtained. Different systems have been proposed to accomplish this.
In one such system the plated strip is guided onto a measuring wheel which rotates continuously with the strip. The wheel carries one or more measuring probes in operative contact with the strip coating on the wheel. This system has limitations because of wheel diameter size, speed of travel, and accurate positioning of the moving specimen on the probe(s).
In another such system, the measuring probe is stationary and positioned on one side of a slide block. The strip is moved across the opposite side of the block, being maintained in contact therewith by a continuously rotating hold-down wheel. This system measures the average thickness of the coating over a length of strip during the time required for measurement. Where the strip is interrupted, consisting of a band of plated segments, the measuring system is interrupted during the intervals between segments, limiting the capabilities of the system with respect to travel speed of the strip.